1. Field of the Invention
The present invention relates to a system and method for the welding of drill bits using robotic apparatus.
2. State of the Art
In the exploration of oil, gas, and geothermal energy, wells or boreholes in the earth are created in drilling operations using various types of drill bits. These operations typically employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a drill string having a drill bit secured to its lower end. As the drill bit drills the well bore, segments of drill pipe are added to the top of the drill string. While drilling, a drilling fluid is continually pumped into the drilling string from surface pumping equipment. The drilling fluid is transported through the center of the hollow drill string and through the drill bit. The drilling fluid exits the drill bit through one or more nozzles in the drill bit. The drilling fluid then returns to the surface by traveling up the annular space between the well bore and the outside of the drill string. The drilling fluid transports cuttings out of the well bore as well as cooling and lubricating the drill bit.
The type of drill bit used to drill the well will depend largely on the hardness of the formation being drilled. One type of rotary rock drill is a drag bit. Early designs for a drag bit included hard facing applied to various portions of the bit. Currently, designs for drag bits have extremely hard cutting elements, such as natural or synthetic diamonds, mounted to a bit body. As the drag bit is rotated, the cutting elements form the bottom and sides of the well bore
Another typical type of rotary drill bit is the tri-cone roller drill bit that has roller cones mounted on the body of the drill bit, which rotate as the drill bit is rotated. Cutting elements, or teeth, protrude from the roller cones. The angles at which the roller cones are mounted are mounted on the bit body determine the amount of cut or bite of the bit with respect to the well bore. As the roller cones of the drill bit roll on the bottom of the hole being drilled, the teeth or carbide inserts apply a high compressive and shear loading to the formation causing fracturing of the formation into debris. The cutting action of roller cones comprises a combination of crushing, chipping and scraping. The cuttings from a roller cone drill bit typically comprise a mixture of chips and fine particles.
There are two general types of roller cone drill bits; TCI bits and milled-tooth bits. “TCI” is an abbreviation for Tungsten Carbide Insert. TCI roller cone drill bits have roller cones having a plurality of tungsten carbide or similar inserts of high hardness that protrude from the surface of the roller cone. Numerous styles of TCI drill bits are designed for various types of formations, in which the shape, number and protrusion of the tungsten carbide inserts on the roller cones of the drill bit will vary, along with roller cone angles on the drill bit.
Milled-tooth roller cone drill bits are also referred to as milled-tooth bits because the steel teeth of the roller cones are formed by a milling machine. However, in larger bits, it is also known to cast the steel teeth and, therefore, “milled-tooth” is the better reference. A milled-tooth roller cone drill bit uses roller cones each having an integral body of hardened steel with teeth formed on the periphery. There are numerous styles of milled-tooth roller cone drill bits designed for formations of varying hardness in which the shape, number and protrusion of the teeth will vary, along with roller cone angles on the drill bit.
Conventional welding techniques used to attach a circular plug to the leg of a milled-tooth or TCI roller cone drill bits that may include arc welding, oxyacetylene welding (OAW) and atomic hydrogen welding (AHW). Currently, manual welding is typically used in the commercial production of roller cone rock bits. Bit legs having roller cones are mounted on a positioning table while a welding torch and welding rod are used to manually weld the plug to the bit leg while either the bit leg or the welder moves from various positions to complete the welding of the plug on the bit leg. The welding process for attaching the plug to a bit leg is difficult due to the circular weld to be made attaching the plug to the bit leg.
Typically, the skill of the individual applying hardfacing determines the quality of the weld. The quality of weld between drill bits varies. Limited availability of qualified welders has aggravated the problem because the welding of the plug to the bit leg is extremely tedious, repetitive, skill-dependent, time-consuming, and expensive.
U.S. Pat. No. 6,392,190 provides a description of the use of a robotic arm in the hardfacing of roller cones, in which the torch is held by a robotic arm and the roller cones are moved on a positioning table. A manual welder is replaced with a robotic arm for holding the torch. The robotic arm and a positioning table are combined to have more than five movable axes in the system for applying hardfacing.
Therefore, there is a need to develop a system and method for welding plugs to bit arms of drill bit consistent with the material and application quality standards obtainable by manual welding.